The present invention relates to a control apparatus and controlling method for an automatic transmission that appropriately changes a rotation input from an engine and outputs it by engaging certain frictional engagement elements from a plurality of the frictional engagement elements in accordance with a speed gear, and more particularly to a control apparatus and controlling method for the automatic transmission performing a down-shift by way of changeover between a first frictional engagement element that achieves a higher speed before a gear shift and a second frictional engagement element that achieves a lower speed after the gear shift in a power-off condition during vehicle travel.
In general, when performing a gear shift by an automatic transmission, a changeover from disengagement (release) to engagement or vice versa of such a frictional engagement element as the clutch is done. At the changeover, it is desirable that the disengagement and engagement of the frictional engagement element should be achieved smoothly and promptly without a shock at the shift. Various kinds of arts or methods, then, are proposed and developed, and they are disclosed, for instance, in Japanese Patent Provisional Publication No. 9-170654 (hereinafter is referred to as “JP9-170654”) and Japanese Patent Provisional Publication No. 2000-110929 (hereinafter is referred to as “JP2000-110929”).
In JP9-170654, an oil pressure to a hydraulic servo, of a frictional engagement element is controlled, and the shock can be reduced. As described in Abstract in JP9-170654, with respect to an engagement side frictional engagement element that is going to be changed from a disengaged (release) condition to an engaged condition, a target oil pressure PTA at the initiation of inertia phase is calculated in accordance with an input torque. And a desired gradient is calculated by this target oil pressure and a predetermined time tTA, then the oil pressure is increased with the calculated gradient as a first sweep-up. Further, a relatively moderate gradient δPTA is calculated and set based on a target rate of change of rotation at a time when an input shaft rpm NT starts changing. When the oil pressure reaches the target oil pressure PTA, the oil pressure is increased with this relatively moderate gradient as a second sweep-up, and the second sweep-up is continued until variations ΔN of the input shaft rpm NT reaches a predetermined shift-start-judgment rpm dNs, which is an rpm that is able to be detected by an input shaft rpm sensor. After that, the oil pressure is feedback-controlled with a predetermined gradient while detecting the variations of the input shaft rpm. Further, a target shift start time and a rate of change of rpm at the time of the target shift start are measured, then the target oil pressure PTA, the gradient δPTA of the second sweep-up section and a target shift start time taim are learned and corrected.
On the other hand, in JP2000-110929, changes in torque input to a transmission is detected whenever the input torque change occurs during the shift performed by way of changeover of the frictional engagement elements. And in the case of occurrence of the input torque change during the shift, working fluid pressures of engagement side and disengagement side frictional engagement elements can be changed to pressures determined according to the input torque after the occurrence of torque change. With this, occurrence of engine racing, shift delay and a large incoming torque can be prevented without excess and deficiency of capacity against the input torque change of the transmission. As described in Abstract in JP2000-110929, during an up-shift by changeover being performed such that an engagement side working fluid pressure command value Pc is increased as shown by a solid line in a drawing and a disengagement side working fluid pressure command value PO is lowered as shown by another solid line, when a transmission input torque Ti changes at a time t2, a lowering preliminary pressure PO1 of PO is changed to a value determined according to Ti after the torque change, and a lowering gradient of PO is changed after the time t2 as shown by a two-dot chain line. When Ti becomes a predetermined value or more at time t5, a torque phase ramp gradient θ5 of Pc is determined, and an increasing gradient of PC is changed from a normal gradient θ1 to the steep gradient θ5 as shown by another two-dot chain line. After that, when Ti changes at time t7, as shown by a two-dot chain line, the torque phase ramp gradient θ3 of Pc is changed to a gradient determined according to Ti after the torque change. When the change of Ti occurs at time t10, a shelf pressure PC1 of PC and a shelf pressure PO1 of PO are changed to values determined according to Ti after the torque change as shown by two-dot chain lines.